1. Field of the Invention
The present invention relates to image signal processing apparatuses and methods, and programs and recording media used therewith, and in particular, to an image signal processing apparatus and method that perform appropriate correction of image blurring in accordance with a characteristic of an image, and a program and recording medium used therewith.
2. Discussion of the Background
In recent years, many digital still cameras each having an automatic focusing function have come into widespread use. The automatic focusing function detects an appropriate focus and performs automatic focusing without user's manual focusing. Although the automatic focusing function enables the user to easily capture images, image capturing may be performed in a state in which, not the original subject whose image to be captured by the user, but the background of the subject is brought into focus. This may consequently cause the image of the original subject to blur.
To correct a picture having a blurred subject image as described above, a technology (see, for example, Japanese Unexamined Patent Application Publication No. 6-68252) in which the image is cleared by performing edge-enhancement sharpening in a blurred portion has been proposed.
In addition, as a method for correcting a picture when considering a blurring model, a technology (see, for example, Japanese Unexamined Patent Application Publication No. 8-272995) in which, when assuming that the pixel levels (observed values) of a captured image are such that the pixel levels (true values) of an image free from blurring are spatially diffused, by writing a model expression between the true values and the observed values and solving the model expression, the true values are estimated from the observed values for image correction.
In the technology disclosed in Japanese Unexamined Patent Application Publication No. 6-68252, a model of blurring caused by shifting in focusing is not considered. Accordingly, information of image details lost due to blurring cannot be reproduced with high fidelity.
In the technology in Japanese Unexamined Patent Application Publication No. 8-272995, the model expression is solved by uniformly setting coefficients concerning portions far from the center of diffusion to be zeroes. When the degree of diffusion is small, the range of diffusion is narrow, and pieces of true-value information concentrates around the center of diffusion. Accordingly, in relation to the uniform setting of the coefficients concerning the portions positioned away from the center of diffusion to be zeroes, no inconsistency occurs. When the degree of blurring is large, even in portions positioned away from the center of diffusion, pieces of true-value information sufficiently exist. Accordingly, by setting the coefficients to be zeroes, inconsistency occurs. In addition, since characteristics of the image are not considered in the case of solving the model expression, in the case of a picture including noise such as JPEG (Joint Photographic Experts Group) noise, there is a possibility that noise may be enhanced to result in deterioration in image. This causes a problem of an inability to appropriately correct the image.